The present invention relates to a plate type heat exchanger, and more particularly to a plate type heat exchanger for exchanging heat between two fluids flowing alternately through adjacent fluid passages between piled plates, which is suitable for such cases where at least one of the fluids flows as a liquid film on a surface of the plate, or is a low-pressure vapor, as an evaporator in a refrigerating machine, or an evaporator or a low-temperature regenerator in an absorption refrigerating machine.
A conventional plate type heat exchanger is of a small size for a heat load, and can cope with an increased heat load by increasing the number of piled plates having the same shape, so that the plate type heat exchanger is frequently used as a heat exchanger.
The conventional plate type heat exchanger is shown in FIG. 16. As shown in FIG. 16, two plates 1, 1xe2x80x2 having opening portions 5, 6 at both ends thereof are piled on each other so as to form a space R1 therebetween, and peripheral portions of the plates are sealed to form a heat exchange element 2. The heat exchange elements 2 are piled on and bonded to each other in such a state that the opening portions 5, 6 communicate with each other, thereby forming a heat exchange structure. This heat exchange structure is housed in a shell, and fluids flow inside and outside the heat exchange elements 2 so as to exchange heat with each other. A corrugated or fin-shaped plate 42 is mounted within the space R1 in the heat exchange element 2 to increase the strength of the plates and promote heat exchange by turbulence of a flow. The upper and lower opening portions 5, 6 are projected in a cylindrical form so as to be fitted to each other.
In this type of heat exchanger, an inlet and an outlet for a first fluid passing through the shell are connected to the opening portions 5, 6. The first fluid flows in parallel through the respective heat exchange elements 2 as indicated by arrows. On the other hand, a second fluid flows from an inlet and an outlet for the second fluid, which are provided in the shell, into a space R2 formed outside the heat exchange elements 2. The outside space R2 can be made wider than the inside space R1. Therefore, when a fluid involving a phase change is used as the second fluid, the heat exchanger can cope with a volume change in accordance with the phase change. Further, the inlet and outlet for the outside space R2 can be made larger than the inlet and outlet for R1. Therefore, the heat exchanger can cope with a fluid that is a low-pressure vapor having a large specific volume. The outside space R2 can be made wider than the inside space R1 depending upon the shapes of projections and depressions of the plates, so that the heat exchanger can cope with even a lower-pressure vapor.
To manufacture such a heat exchanger, the turbulence plate. 42 is mounted and positioned on the upper plate 1. Then, the lower plate 1xe2x80x2 is placed on the turbulence plate 42, and the peripheral portion of the lower plate 1xe2x80x2 is folded to be bonded to the upper plate 1, for thereby forming the heat exchange element 2. Next, the adjacent heat exchange elements 2 are connected to each other so that cylindrical communicating portions 7 are fitted to each other, for thereby assembling a heat exchange structure. The resulting heat exchange structure is incorporated into a shell 9.
Such a conventional plate type heat exchanger requires three components for constituting the heat exchange element 2, and thus involves problems that manufacture and management of the components are burdensome and costly.
FIG. 17 is an exploded perspective view of a plate type heat exchanger in which a plurality of heat exchange elements 2 are piled on each other and housed within a shell 9.
With a plate type heat exchanger having a structure shown in FIG. 17, when the number of the heat exchange elements 2 is increased, heat exchange capacity can be improved. Further, a liquid having a large specific volume, such as a vapor or a vapor-liquid two phase fluid, can be used as an external fluid. In FIG. 17, the reference numeral 3 denotes an opening portion constituting an introduction passage for an external fluid, the reference numeral 4 an opening portion constituting a discharge passage for the external fluid, the reference numeral 5 an opening portion constituting an introduction passage (supply passage) for an internal fluid, the reference numeral 6 an opening portion constituting a discharge passage (supply passage) for the internal fluid, and the reference numeral 7 a cylindrical communicating portion.
It has been known that when the plate type heat exchanger having the structure shown in FIG. 17 is used in an absorber or an evaporator of an absorption refrigerating machine, for example, the refrigerating machine can be downsized.
In these heat exchangers, since an internal fluid is generally supplied to a plurality of plates, as shown in FIG. 17, the heat exchanger is used in such a state that an inlet and outlet of the heat exchanger and an inlet and outlet (ports) of the plates are connected to each other, and the ports of the plates are connected to each other, via supply passages such as supply pipes, discharge pipes, and communication pipes for a working fluid. In many cases, the supply passages are provided on heat transfer surfaces of the plates because of productivity in such a manner that the supply passages are faced to and communicate with each other when the plates are piled on each other.
In this case, when the flow rate of the internal fluid is increased, it is necessary to thicken the supply passages 5, 6. Therefore, the supply passages provided on the heat transfer surfaces occupy the heat transfer area, and simultaneously prevent a flow of the external fluid.
Particularly, as shown in FIG. 18, in such cases where the external fluid flows as a liquid film for performing heat exchange, as an absorber or an evaporator in an absorption refrigerating machine, if wide supply passages are provided, then it is difficult to supply the fluid to entire regions below the supply passages and hence the regions are not effectively used as the heat transfer surface in many cases. In FIG. 18, a hatched area represents regions of the flow of the fluid, and portions a below the supply passage 5, 6 without hatching represent regions of no fluid flowing.
Generally, in the plates, there is provided a fluid distribution portion having radial passages for uniformly distributing the fluid supplied from the ports to the plates. As the supply passage becomes wider, the fluid distribution portion becomes more complicated and larger, so that the fluid distribution portion occupys a larger area of the heat transfer surface.
Even if supply passages having an elliptic or rectangular shape are used to solve the above drawbacks, such supply passages increase cost and make productivity worse. Besides, a flow in a direction of the minor axis of the shape of the supply passage is worsened, although a flow in a direction of the major axis can be improved. This is not a solution to the problems.
The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a plate type heat exchanger having a highly efficient function of heat exchange, which requires a small number of components and can reduce cost of production and assembly.
It is another object of the present invention to provide a plate type heat exchanger having a highly efficient function of heat exchange, which can be manufactured by a small man-hour and is likely not to prevent a flow of a working fluid even at a high flow rate.
To attain the above objects, according to a first aspect of the present invention, there is provided a plate type heat exchanger having a heat exchange element composed of two plates for exchanging heat between a fluid flowing inside the heat exchange element and a fluid flowing outside the heat exchange element, characterized in that: the two plates have a plurality of depressions, and the depressions are brought into contact with and bonded to each other; peripheral portions of the plates are sealed to form a space in which a fluid flows and constitute a heat exchange element having opening portions at both ends thereof; and the heat exchange elements are piled on and bonded to each other so that the opening portions communicate with each other.
In the plate type heat exchanger, it is desirable that the depressions of the plate are formed in a circular shape or a horizontally elongated elliptic shape, and a contacting portion between projections produced by the depressions has a plane surface of at least 0.3 mm in width.
The peripheral portions of the two plates may be brought into contact with each other along whole peripheries upon piling, and contacting portions between the peripheral portions may be sealing by bonding. At least one of the opening portions at both ends of the plate may be composed of a plurality of opening portions.
According to a second aspect of the present invention, there is provided a plate type heat with opening portions at both ends thereof are piled as a set on each other to constitute a heat exchange element, a plurality of the heat exchange elements are piled on each other to form a space between the two plates constituting the respective heat exchange elements as a passage for a first fluid, and a space between the adjacent heat exchange elements as a passage for a second fluid in heat exchange relationship with the first fluid, and the plate serves as a heat transfer surface for both of the fluids, characterized in that: one of the plates has a contacting portion with the other plate at a peripheral portion of the plate and at the opening portion; when the two plates are piled as a set on each other, only the peripheral portions of the plates are brought into contact with each other; when the plates are pressed by an applied force until the projections and depressions of the two plates are brought into contact with each other, the contacting portions of the peripheral portions deform to be brought into surface contact with each other along whole peripheries; when the adjacent heat exchange elements are piled on each other in such a manner that the opening portions are aligned with each other, only the peripheral portions of the opening portions are brought into contact with each other; and when the plates are pressed by an applied force until the projections and depressions of the plates of the heat exchange elements are brought into contact with each other, the contacting portion of the respective peripheral portions of the opening portions deform to be brought into surface contact with each other along whole peripheries.
In the plate type heat exchanger, it is desirable that all of the plates are integrated by brazing the contacting portions at the peripheral portion and at the opening portions of the plates. The projections and depressions of the plate may be formed in a shape inclined to one direction. The projections and depressions of the plate may be formed as spot-like projections and depressions having a circular or other cross section, and the height of the projections may be larger than the depth of the depressions when the heat exchange element is constituted.
Further, it is desirable that the plate has a rising portion so that the rising portion is fitted into the opening portion of another plate when the plates are piled on each other.
According to a third aspect of the present invention, there is provided a plate type heat exchanger having a plurality of hollow plates in a shell, each of the hollow plates composed of two thin sheets and having an internal space enclosed at an outer peripheral portion thereof, an introduction passage and a discharge passage for allowing an internal fluid to flow inside the plates being connected to the plates, an introduction passage and a discharge passage for allowing an external fluid to flow within a space between the outside of the plates and the shell being connected to the shell, characterized in that: at least one of the introduction passage and the discharge passage for the internal fluid connected to each of the plates is composed of a plurality of passages.